Genes that might control the determination of a specific cell lineage and genes that might regulate the progression of cells through that lineage have not been identified. We propose a series of DNA and RNA microinjection protocols based largely on recombinant DNA technology to identify genes that "regulate" the developmental transitions occuring during the later stages of erythropoiesis and granulopoiesis and the early stages of erythropoiesis. Since we believe that the action of these types of genes is both reflected and recorded in chromatin structure, a major effort will be devoted to the study of DNase I and S1 hypersensitive (H.S.) sites; and the role, if any, of H1 in gene expression. Specific experiments are proposed to study in situ the patterns of chromatin assembly and segregation. Continuing efforts to develop methods to study chicken lampbrush chromosomes should enable rapid gene localization and localization of specific proteins. These chromosomes may also be useful "reagents" for morphological visualization of nuclear structures previously seen only by biochemical methods.